This invention concerns a suction device for autotransfusion of blood during surgery.
Homologous blood transfusions, i.e. the transfusion of compatible blood from other persons, involves some risk of the transfer of illnesses such as hepatitis and AIDS. They can also cause immunodepression and reduce the patient's natural defences. Finally, some patients refuse to receive the blood of other persons because of their religious beliefs.
For these reasons autologous transfusion or autotransfusion is widely used, i.e. transfusion of the patient's own blood. Autotransfusion can be delayed in the sense that blood is taken from the patient and stored for subsequent transfusion into the same person. This is not always possible, however; the transfusion may be required urgently, for example. In this case autotransfusion during surgery can be used, in which blood lost by the patient during a surgical procedure is collected and transfused into the patient.
The device conventionally used for autotransfusion during surgery includes a suction canula connected by a flexible tube to a depressurised blood storage vessel. The suction canula is also connected to an anticoagulant storage vessel. During the surgical procedure blood lost by bleeding in the operative field is aspirated by the canula, mixed with the anticoagulant in the canula and collected in the storage vessel from which it is transfused into the patient.
A basic technical problem encountered with autotransfusion during surgery is to mix the blood and the anticoagulant in proportions that lie within the correct range. With anticoagulants such as CPD (citrate-phosphate-dextrose), for example, or heparin or a mixture of heparin and CAD (citric acid-dextrose), where a typical anticoagulant solution for 1 liter of blood serum comprises 60 ml of AB 16 plus 30 000 units of heparin, the ratio of the volume of anticoagulant to the volume of blood collected has to be around 1:7, the optimum ratio, and must not exceed 1:5 or fall below 1:10. If the ratio is too high the composition of the blood is too severely changed for the blood to be transfused while if it is too low there is insufficient anticoagulant in the mixture to prevent the blood from coagulating. At a ratio of around 1:7 the chemical, enzyme and blood corpuscle morphology composition of the blood are only slightly altered and the concentration of the anticoagulant is sufficient to prevent coagulation. With other anticoagulants the range of permissible values for the ratio of the volume of anticoagulant to the volume of blood can be different.
General information on autotransfusion can be found in the following publications:
--ADHOUTE, NAHABOO, LANCELLE, MORA, ROUVIER--Autotransfusion en pratique chirurgicale. J. Chir. 1977, 114, 17-24,
--ADHOUTE, NAHABOO, LANCELLE, MORA, ROUVIER--Autotransfusion: XIIIth World Congress of the International Cardiovascular Society. 30 August 30 September 20, Tokyo, Japan.
--ADHOUTE, NAHABOO, REYMONDON, ORSONI--Application de l'autotransfusion en chirurgie vasculaire reglee, Lyon Chir., 1978, 74, 50-62,
--ADHOUTE, NAHABOO, LANCELLE, MORA, ROUVIER, BLEYN, ORSONI--Autotransfusion in Surgical Practice, Cardio. Vasc. Res. Center Bull, 1979, 18, 40-15, Texas Medical Center, Houston, Tx. 77030--USA,
--ADHOUTE, HENIN--Economie du sang en chirurgie. J. Chirurgie, Paris, 1980, 117, 713-722.
--AUTOTRANSFUSION: Proceedings of the First International Autotransfusion Symposium: Apr. 24-25, 1980, Blood Bank Laboratories, University of Maryland School of Medicine, Md. U.S.A. Elsevier/North Holland, N.Y., Amsterdam, Oxford,
--ADHOUTE, AYOUB, REYMONDON, GAUTHIER--Autotransfusion peroperatoire d'hemoperitoines en Chirurgie traumatique d'urgence: J. Chir., Paris, 1988, 123, N 2, pp. 92-96, Masson, Paris, 1988,
--ADHOUTE--Autotransfusion: Utiliser son propre sang. Springer-Verlag France, 26 rue des Carmes, Paris, 1989.
--ADHOUTE--Autotransfusion: using your own blood. Springer-Verlag, Heidelberg, Federal German Republic, 1991.
A solution to the technical problem of controlling the concentration of anticoagulant in the aspirated blood is proposed in French patent application No 2 503 566. This document describes a suction canula for autotransfusion during surgery with a suction nozzle at one end and the opposite end connected by a flexible tube to a blood storage vessel depressurised by a vacuum source. A tube connected to an anticoagulant solution storage vessel opens into the canula near the suction nozzle: thus if the suction nozzle aspirates air the pressure drop in the canula at the anticoagulant entry is too small for anticoagulant to be aspirated; however, if the suction nozzle is immersed in blood in the operative field the suction of this blood causes a greater pressure drop in the canula and anticoagulant is therefore aspirated into it. The dimensions of the anticoagulant feed tube as compared to those of the suction nozzle are such that the ratio of the anticoagulant to the volume of aspirated blood is approximately 1:7. However, when the canula is not being used to aspirate blood it continues to aspirate air and may therefore aspirate lightweight materials around the operative field (the gown of a person near the operative field, for example) which could block the suction nozzle: the pressure drop in the canula is then increased with the result that anticoagulant is aspirated but no blood. The same thing can happen during the suction of blood if any debris obstructs the suction nozzle and the user does not notice right away. If debris enters the suction nozzle of the canula the user may not be able to remove it quickly, in which case the vacuum source will have to be switched off to stop the flow of anticoagulant. In the meantime a relatively large quantity of anticoagulant may have been aspirated into the blood storage vessel with the result that the blood in it may be unfit for use. Also, when the canula is not aspirating blood it continues to aspirate air which then enters the blood storage vessel before it is aspirated therefrom by the vacuum source. Dust or microorganisms in suspension in the air can then collect in the blood or in a filter of the storage vessel so that the latter is no longer sterile. Furthermore, this constant flow of air in contact with the blood in the storage vessel is a source of haemolysis: the blood transfused into the patient is then lacking in red corpuscles.
U.S. Pat. No. 3,964,484 also describes a suction canula for autotransfusion during surgery which seeks to maintain a constant anticoagulant to aspirated blood volume ratio. This canula has a suction nozzle at one end and the opposite end is connected by a flexible tube to a blood storage vessel depressurised by a vacuum source. The canula also has an air vent and is connected to an anticoagulant feed passage which opens into the canula near the suction nozzle. The anticoagulant feed passage includes a valve to shut off the passage if the canula is not depressurised and to open it when the canula is depressurised. To this end the valve includes a flexible, elastic diaphragm communicating on one side with the interior of the canula and having the other side pressed elastically against a plate onto which the anticoagulant feed passage opens. If the canula is aspirating air through the suction nozzle and/or through the vent the pressure drop inside it is small and the flexible diaphragm of the valve remains elastically pressed against the plate and shuts off the anticoagulant feed passage. When the user shuts off the air vent and immerses the suction nozzle in blood the latter is aspirated and the resulting pressure drop in the canula causes the flexible diaphragm to be lifted away from the plate to open the anticoagulant feed circuit.
This suction canula also has its drawbacks:
1. When blood is not being aspirated the canula aspirates air continuously and this air enters the blood storage vessel, causing the problems mentioned above.
2. While blood is being aspirated the suction canula may be totally or partly blocked, by various kinds of debris, for example; the user cannot detect this immediately and there may therefore be a period in which anticoagulant is aspirated but no blood, or less blood; this may make the blood already aspirated unusable for the reasons explained above.